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December 06, 2012

Feeling Disgust May Enhance Our Ability to Detect Impurities

Disgust – it’s an emotion we experience when we encounter things that aredirty, impure, or otherwise contaminated. From an evolutionary standpoint,experiencing the intense, visceral sense of revulsion that comes with disgustpresumably helps us to avoid contaminants that can make us sick or even killus. But new research suggests that disgust not only helps us to avoidimpurities, it may also make us better able to see them.

If something looks dirty and disgusting, we typically assume it’scontaminated in some way; when something is white, however, we are more likelyto assume that it’s clean and pure. Research has shown that people from manydifferent cultures hold this association between lightness and purity, whichmay explain why we prefer white teeth, white operating rooms, and whiteporcelain bathroom fixtures.

“In the psychology of purity, even the slightest deviation from a pure state(i.e., whiteness) is an unacceptable blemish,” observe psychological scientistGary Sherman and his co-authors.

They hypothesized that if feeling disgust motivates people to create orprotect pure environments, it may also lead them to prioritize the light end ofthe visual spectrum. For people trying to preserve cleanliness and purity, theability to distinguish even slight deviations from a light shade like white maybecome particularly important.

Sherman, who is now at Harvard University’s KennedySchool of Government, and his co-authors investigated this hypothesis in threestudies, in which they tested participants’ ability to make subtle gray-scalediscriminations in both ends of the light spectrum. Their findings arepublished in Psychological Science, a journal of the Association forPsychological Science.

In their first study, 123 college students were presented with sets ofrectangles. In each set of four rectangles, one rectangle was either slightlydarker or slightly lighter than the others. The participants were asked toindicate which of the four rectangles in each set was different from the otherthree. After completing the discrimination task, they completed a survey thatmeasured their overall sensitivity to disgust.

In general, the students were better at identifying the rectangle that stoodout when the rectangles were presented on the dark end of the visual spectrum.But the researchers observed a significant relationship between participants’performance on the light end of the spectrum and their levels of trait disgust– people who showed higher sensitivity to disgust also showed betterperformance on the light end of the spectrum relative to the dark end.Importantly, this effect was specific to disgust, as there was no suchrelationship between participants’ levels of trait fear and theirdiscrimination performance.

These findings were confirmed in a second study, showing that students whoreported greater disgust sensitivity were better at distinguishing a faintnumber set against a background of a nearly identical shade presented on thelight end of the visual spectrum relative to the dark end.

Based on these findings, Shermanand his co-authors wondered whether disgust might actively influence whatpeople perceive. Based on the idea of perceptual tuning, they hypothesized thatinducing disgust would actually “tune” participants’ visual perception,enhancing their ability to discriminate among small deviations in lightness.

In the third study, participants were presented with a slide show ofemotional images designed to elicit either disgust (i.e., images ofcockroaches, trash) or fear (i.e., images of a handgun, an angry face). Theythen completed another perceptual discrimination task.

Just as in the first two studies, greater trait disgust predicted betterperformance on light-end trials relative to performance on dark-end trials. Butthe emotional images had different effects depending on the participants’disgust sensitivity. For participants who were low on trait disgust, viewingdisgusting images seemed to have no effect on their discrimination performanceon either end of the spectrum. For participants who were highly sensitive todisgust, however, viewing disgusting images significantly enhanced theirperformance on light-end trials.

“Research on the experience-altering nature of emotion has typically focusedon nonperceptual experience, such as changes in cognitive appraisals. It isclear, however, that these influences extend to perception,” the researchersconclude.

Together, the three studies provide evidence for an interactive relationshipbetween disgust sensitivity and perceptual sensitivity that may ultimately helpus detect and avoid the germs, toxins, and other contaminants around us.

This research was co-authored by Gerald Clore of the University of Virginiaand Jonathan Haidt, who is now at the New York University Stern School ofBusiness.